Flashcards in Post Deck (57):
What are the indications for a post crown?
Insufficient coronal dentine remains to support a conventional style prep for a crown
What is the purpose of the post?
This provides retention
What is the pyrosis of the core?
This replaces the lost dentine to provide diffidence height and parallelism for crown retention
When are post crowns indicated?
Mainly anterior teeth
Post root treatment
Insufficient tooth structure or enable crown prep
Augmentation of retention is required
What are the type of post core systems?
Direct vs indirect
Prefabricated vs custom made
Smooth vs patterned
Metal vs composite fibre
Active vs passive
Conventional mechanical engineering strength principles vs biomimetic principles
Which out of parallel or tapered posts are more tentative?
Which is the disadvantage with parallel posts?
Prep can result in perforation
What are the advances and disadvantages of tapered posts?
Less Risk of perforation during preparation
But can exert a wedge effect on the tooth which could split the root
How can we modify the surface texture?
Threaded: most retentive
Serrated: most commonly used
Smooth : less retentive
Name an example of a threaded post and what are the advantages and disadvantages?
Radix anchor and dentatus screws
AD: offer greatest retention
Dis: threads lead to stresses and increase likelihood of root fracture, they are wife posts which wedge the root apart.
Which type of posts cause the most stress and Increaed risk of failure?
Tapered and threaded posts
Which type of post surface do we usually use?
This enables the cement to interlock
Why do we make separate posts and cores for the crown?
To aid retrievability
And enable ferrule effect where sufficient coronal dentine
What do we need to consider when placing a post crown?
Perio: perio disease and plaque control
Restorative ability: condition of remaining teeth, caries, how much remaining tooth structure
Occlusion: tilting or over eruption of adjacent teeth into space, presence of wear facets, evidence of para function, guidance of tooth in protrusion or lateral excursions
Endo: outcome of endo treatment?
What special investigations would you need for a post crown?
Signs and symptoms
Articulated study models
What are the absolute contradictions ?
Vertical root fracture
What are some salvageable contraindications to a post?
Caries: restore first
Perio: stabilise first
Subginginval margin: consider crown lengthening
Insufficient space for final restoration: create space
Previous perforation: repair
Which things would be considered as pushing the boundaries with regards to post?
Insufficient coronal structure for a ferrule
Using the tooth as an abutment for a fixed or removalble prosthesis
What is a ferrule??
Circumferential supragingival core of metal to prevent the root from splitting
Where should the crown margin be placed ?
2mm apical to core margin
What are the ideal post and core dimensions?
At least 4.5mm GP
At least 1mm dentine
Post: crown ratio at least 1:1 ideally 1.5:1
From crown margin to top of ferrule should be 3.5mm
What could you consider doing before you take your impression?
Consider applying glass ionomer or zinc oxide cement to seal GP but not if using composite
Which cement should we use to cement the post im?
What kind of seating action should you use to cement the post?
A pulsing action
What is the disadvantage of using zinc Polycarboxylate?
Low compressive strength
What is the disadvantage of using GIC?
Propogation of cracks
What is the disadvantage if using resin?
Lack of retrievable
Where are voids most significant and least?
Least: mid third
Most: apical or coronal
What material could you use as a core?
Metal: NiTi: core is made in lab
Composite: for fibre composite system
GIC not strong enough
What are the two broad choices for post and core?
Customised metal post and core
Fibre post and core
What are the advantages and dis of a metal post and core?
AD: tried and tested with good results when used appropriately , crown to root angle can be adjusted, strong even in think section, removal possible
Dis: post and root can fracture, can be difficult to remove, Appearnce of metal through tooth, possible corrosion, staining of dentine, rigidity greater than dentine, possible leakage of temp post crown, susceptible to impression error
What are the advantages and disadvantages of a fibre composite post and core?
AD: reduced number of visits, no temporary postcore, metal free, god light transmission, adhesive technology, potentially biomimetic, maybe possible to use shorter posts due to bonding, bind possible strengthens tooth, less likely to fail due to root fracture
Dis: adhesive technology sensitive and bond weak link
What are the post factors that will affect the longevity of the tooth?
Type of post
Design of post
Presence of ferrule
amount of remaining coronal and root structure
Tooth used as an abutment
How do posts fail?
Endo: inadequate endo, host healing vs virulence of pathogen, leakage due to poorly fitted post, poor temporary
Root fracture: post too short, post too long, post too narrow,active, tapered, post not following anatomy, inadequate dentine, no ferrule
Loss of Retention: post too short, post and core poor fit, weak cement and wrong method of cementation, difficult to bond to root dentine, traumatic occlusion
Separation: casting porosity at narrowest point between post and core, post too narrow and high stress applied, lab casting errors
How do you remove metal posts?
1. Ultrasonic peezo scaler to loosen cement
2. Trephine from masseran kit rotated anticlockwise to cut a channel around post to 50% of its length and remove with smaller trephine
How do you remove fibre posts?
What are the 7 stages to post prep?
1. Removal of GP
2. Coronal prep
3. Post space preparation and antirotatjon
4. Achieve ferrule
6. Temp crown
7. Cement post and core. Cement crown. Separate entities for retrievable
How much GP should you remove?
1. Length of post must be at least the same height as crown
2. Leave at least 4mm GP
3. Extend to beyond centroid
4. 2/3 of root length
5. Long as possible with 1mm dentine around
What must the tip of post be supported by and why?
The root structure to prevent a crow bar effect
How do you remove GP?
Select gates glidden bur and set to correct length and remove GP
What should the coronal prep be like?
Needs to be like a conventional prep with a labial shoulder which is placed in the gingival crevice and the Palatal shoulder is placed at the margin. Needs to be at least 1mm dentine around the post space to avoid fracture in function and on die material in the lab
What must be incorporated in the post space prep?
What are the components of the para post kit?
Smooth impression post
Serrated burn out post
Aluminium temporary post
What type of system is the para post kit?
A hybrid contains both prefabricated and custom made components
What are the prefabricated components of the para post kit?
Use drills to prepare the canals and use a plastic burn out post to fit post space
What are the custom made components of the para post kit?
Core made in eitherwax or duraly invested in type 4 gold alloy
What effect does the ferrule effect have in the impression?
Makes recording the impression easier
Which impression technics are there?
Indirect impression with oppsing alginate.
Direct with duraly impressioon
How does the indirect impression technique work?
One end of the smooth impression post is flattened outside th mouth to aid retention in impression material the upper part of the impression post and head are coated in adhesive
How does the direct impression with the duraly work?
Serrated plastic burnout post inserted into space and then coat dentine with a separting medium
Duraly then shaped and once polymerised is finished with instruments eg disk .
Duraly and burnout post come off in one piece and cause in type 4 gold
For both the direct and the indirect impression technique, what must you place in the post space to temporise it?
The aluminium post which has been scored diagonally to provide Antirotation
How much must the aluminium post protrude from the tooth?
How do you temporise the crown?
Using a directa crown and trim
How do you remove the GP for the composite fibre post?
Using peeso reamers which act like GG
How much fibre post should be protruding from the tooth?
What must you do to the post before cementing properly ?
Must decontaminate in alcohol